FTA: There are plenty of scientific reasons why skyscrapers don't-and probably won't-have trees, at least not to the heights which many architects propose. Life sucks up there. For you, for me, for trees, and just about everything else except peregrine falcons. It's hot, cold, windy, the rain lashes at you, and the snow and sleet pelt you at high velocity. Life for city trees is hard enough on the ground. I can't imagine what it's like at 500 feet, where nearly every climate variable is more extreme than at street level.

So what they're saying is that a REALLY, REALLY, REALLY tall skyscraper might have a treeline?

First, most of those renderings are BS anyway. They are for marketing, not construction. Most of the stuff like that isnt removed from the project because its not possible, but it gets VE'd out because the developer doesnt want to spend a dime on something he cant lease out.

Remember when the WTC #1 was going to have a "Vertical Gardens of the World" component where each set of floors would be a different climatic region of the world.

and instead we end up with yet another glass shoebox because "OMG rentable space!"

Secondly, "Life for city trees is hard enough on the ground. I can't imagine what it's like at 500 feet, where nearly every climate variable is more extreme than at street level. "

Everybody knows trees can exist at 501 feet or if the weather is a bit extreme

The biggest problem with having trees on skyscrapers isn't the weather or the wind.

It's the weight.

Trees weigh a LOT - per square foot. Then, of course, you need a nice thick (and heavy) bed of dirt for them to live in (and anchor against the wind). Then there's the wind loading problem - an "open with trees" building a few hundred feet high would have several times the horizontal wind load of a normal glass/steel/stone building.

Skyscrapers are large, but they're basically not designed to hold up much more than their own weight, some furniture, and a moderate number of people per floor. They have to specifically design buildings that hold more than "office density" numbers of people.

To engineer a "tree-friendly skyscraper," you'd need to make the whole structure about three to five times as strong as one merely designed to hold people + furniture. $$$$

Then, of course, there's the "things fall off of trees a lot" problem. A twenty pound branch falling off during a wind storm in your back yard is problematic. One falling off a five hundred foot skyscraper is lethal...

cirby:The biggest problem with having trees on skyscrapers isn't the weather or the wind.

It's the weight.

Where are you pulling your numbers from? The soil is heavy but it isn't going to increase the load by 3-5 times even when soaking wet. The problem is cost, and the liner you need to prevent leaks is steep in price.

It's the wind - and that tends to go hand in hand with being 2700 feet above the GROUND, wherever that ground may be.

Yep. I was going to say... 500 feet above sea level is not the same as 500 feet above ground level.

I do like the green roofs though. I work with a building or two here in Washington DC which have them and I think they're neat. They look nicer and the heating and cooling benefits can't be bad. Trees would be even neater, I'm sure, I just can't imagine that the roots wouldn't be a huge problem. Tree roots are strong, and over time they can destroy a lot of shiat.

thecpt:They do know about vegetated roofs right? still waiting for a LEED project where I get to do one.

You may wait a long time. The cost of a green roof can always be better spent else where. The only reason to go with them is either aesthetics or as an amenity (if you have no land, like in NYC, or demand for a private yard, like a condo penthouse, then they can pencil out).

HVAC benies are grand, but 12" of foam is cheaper and better in almost every technical way (I'll use a water tank and PEX tubing if I want thermal mass - more controllable).

simple issue is simple... the weight of one of those trees is equivalent to a person and everything they own.The weight of a tree that actually has a root system able to support it to look that good is even higher.

Water weighs a 62.43 pounds a cubic foot. Wood and soil are slightly lighter, but to have a roof garden you have to build carefully and use strong materials. Many of the buildings here have some sort of roof garden, including the Rideau Shopping Centre, and there are terraces on some government buildings which make them vaguely look like the Hanging Gardens of Babylon.

The apartment building shown would probably have quieter balconies and would be great in the in the summer because trees shade and cool (not just with shade but also with evaporation).

Some of the apartments here have trellises. Italians sometimes have vines on trellises over their patios or driveways, on which they grow grapes to make homemade wine. They work well on balconies also because they provide shade, privacy and greenery with a small footprint.

There are several advantages to planting on buildings--cleaner air, noise-reduction, insulation against the heat. I'm all in favour of incorporating grass, trees and flowers into denser urban environments. I visited Florence, an ancient city with no greenery downtown, and although it is a very walkable place, you miss the plants, even the spindly, sickly trees that you find in modern urban areas. Some of the vertical gardens you see on Treehugger and other sites are beautiful. Many kinds of herbs and flowers can make a blank wall a showcase of meadow flowers and scented garden herbs instead of low grade graffiti.

The only bad urban horticulture is grow ops. Besides using tremendous amounts of power (often stolen) they are very toxic. They have been found in urban apartment buildings. Marijuana-growing is an outdoor sport, as my Mother would say.

Trees can cut your heating and cooling bill by 20%. A green roof is a lovely, environmentally friendly but expensive alternative to good insulation. I'd definitely consider one if I didn't have to mow it or weed it.

Old world thatched roofs (which are about two or three feet thick, maybe more) often developed a top layer of soil. Old houses were effectively eco-systems rather than sealed boxes full of chemicals. I know the downside to the old ways as well as the new, but all in all, the old ways were better if time-consuming and maintenance-heavy. But then you spend more time paying for and cleaning "labor-saving" devices than the devices ever save.

Surpheon:You may wait a long time. The cost of a green roof can always be better spent else where. The only reason to go with them is either aesthetics or as an amenity (if you have no land, like in NYC, or demand for a private yard, like a condo penthouse, then they can pencil out).

I used to work around Philly where they have water runoff problems so the city gave thousands in credits if you had a green roof. I missed that ship though.

thecpt:Where are you pulling your numbers from? The soil is heavy but it isn't going to increase the load by 3-5 times even when soaking wet.

Actually, it will. Dirt is heavy, and people (in a normal office environment) are relatively light. Between the weight of the heavy concrete planters, the dirt, and the water in the dirt, each tree will be the weight equivalent of ten to twenty people.

You can't plant a tree in a foot or three of dirt and expect it to get to the size of the ones you see in those proposals. Even a small tree needs a good five or six feet of dirt. You might be able to get away with that for a rooftop garden (which usually features a lot of low-depth plantings and such, with a few deeper spots for very small trees), but doing that for multiple floors? You're going to double (or more) the cost of the building, even with just a few floors devoted to trees.

The ones in the linked article are probably not going to do well, though - the planters they have them in are shallow, and they're going to have severe root problems. Smaller root systems in fixed planters = more chance of trees dying or blowing over in high winds. I've seen ground-level trees like that get knocked right over in light winds - imagine what can happen when the higher-than-ground-level gusts start to hit...

To get the "nice place, I like the greenery" effect, you'd be better off with a bunch of low-impact plants in shallower soil beds. Bushes and shrubs rather than heavy trees.

Of course, the other effect is that the towers in the article can only hold about 1/4 of the number of residents that a non-tree tower can (look how thin that internal occupancy core is, compared to the overall structure). Nice place to hang out, but it's going to be really, really expensive per square foot to live there.